This invention relates generally to well pumping units and more particularly to an improved safety brake assembly for shutting down operation of the pumping unit in the event of failure of one or more components on the lift side of the pumping unit, when under load. Such failures, although rare, have disastrous consequences both for personnel in the area and the equipment being used.
The present invention has utility with a wide variety of well pumping units, particularly of the kind that I have developed. In general, such a well pumping unit includes a tower mounted on a base platform with a top platform surmounting the tower, a source of power and a winding drum on the base platform, a lift belt made of conveyor belting from the winding drum up the tower to a spool mounted on the top platform and then extended downwardly and connected to the polish rod of a well pump, and a reversing mechanism associated with the power means to reciprocate the belt and thus the polish rod and thereby operate the pump. A counterbalance or counterweight is provided in that portion of the drive belt between the spool and the winding drum so that power requirements of the pumping unit are kept to a minimum.
The need for a fail safe mechanism is particularly acute during a lifting stroke of the pumping unit. The polish rod load may well be in the area of, for example, from 10,000 to 30,000 pounds and the counterbalance will be weighted only somewhat less than the polish rod load. If that portion of the lift belt between the spool on the top platform and the polish rod should fail or if one or more of the polish rod, rod string and sucker rod components of the well pump should fail, the lift belt will unravel from the spool as the counterbalance falls to the base platform; the possible, disastrous consequences are self-evident. Accordingly, this invention provides a mechanism for immediately locking or trapping the lift belt in place in the event of a failure as just described.
A brief description of the need for, and development of, well pumping units is in order. In the early life of a well, reservoir pressure alone may be sufficient to raise the oil to the surface, providing local regulatory authorities permit such a procedure. In any event, eventually the oil will have to be pumped to the surface to be recovered. The most common variety of pump employed for this purpose is a walking beam pump having a nominal stroke distance of from about seven to twelve feet. Such pumps are inefficient and inoperable in wells having depths approaching one, two or more miles. In such cases, rod stretch alone will approach and eventually equal the stroke distance of a walking beam pump, making such a pump completely useless.
Accordingly, longer stroke well pumping units, particularly useful in deep wells, have been developed, some of which have stroke lengths of thirty-two feet or more. One example of such a prior art long stroke pumping unit is the "Oilwell" Model 3534 Long Stroke Pumping Unit, manufactured by Oilwell, a division of United States Steel. The unit includes a central tower having multiple guides to stabilize the structure, a complex multi-strand cable crown block assembly suspending the rod string and a variable capacity counterweight and, of course, a prime mover. Several safety systems are provided, including an automatic air brake system controlled by an overspeed governor flyweight responsive when the counterweight exceeds a predetermined, acceptable downward speed. Other safety features include interlocked controls and automatic breaking in the event of an air loss or power failure. Both the pumping unit and the safety features provided are complicated and quite expensive.
My own prior U.S. Pat. No. 3,248,958, discloses and claims a wire line deep well pumping apparatus and a safety brake system was developed for this deep well pumping unit which included a somewhat complex system for jamming a cam against the wire lines in the top platform mounted sheaves in the event of rod string failure, thus preventing the counterweight from falling. In my prior U.S. Pat. No. 3,483,828, which also disclosed a deep well pumping unit, a braking system was generally described which was actuated in the event of failure; the brake could also be used to hold the apparatus in a static position while the well was being serviced.
Other long stroke, deep well pumping units that I have invented are disclosed in my prior U.S. Pat. Nos. 3,483,828; 3,538,777; 3,777,491; 3,792,836; and 3,986,564. A hydraulically operated deep well pumping unit employing a single, wide strap or belt as the operative connection between the winding drum and the polish rod of the pump is shown in FIGS. 4 and 5 of my above-mentioned U.S. Pat. No. 3,777,491. A yoke assembly somewhat similar to that disclosed and claimed below is also disclosed in FIG. 5 of that same patent.
However, the prior art does not disclose a completely reliable, fail safe mechanism for use with well pumping units of the type above described and which is of uncomplicated structure and requires no power means in order to be operated. Additionally, the prior art does not disclose the yoke assembly herein disclosed and claimed for attaching the lift belt above described to the polish rod upper end. Of course, this invention is useful in wells of all depths which particularly enhances the universality of its application.